JPH0884133A - Optical link - Google Patents

Abstract

PURPOSE: To provide an optical link capable of attaining simlification, economical improvement and size reduction for a radio control station and constructing a highly flexible radio signal distribution system due to the simplification of a radio base station. CONSTITUTION: A radio control station converts a high frequency signal to be sent to an information terminal into a light signal by frequency multiplexing through a photoelectric converter 37 and transmits the light signal to respective radio base stations 101 to n. Each of the radio base stations 101 to n converts the light signal into a high frequency signal by a photodetector 38, amplifies the high frequency signal by a high frequency amplifier 39, selects required frequency by a frequency selecting circuit 40, and then radiates the frequency- selected signal to space through a circulator 43 and an antenna 44. On the other hand, a high frequency signal from the information terminal is received by the antenna 44 in each of the stations 101 to n and inputted to an optical external modulator 41 through the circulator 43 and the amplifier 42 to modulate the light carrier output intensity of the light signal outputted from the photodetector 38. A photodetector 45 in a radio control station reproduces a high frequency signal multiplexed by respective radio base stations 101 to n.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless signal distribution system in which an optical fiber link and a wireless link are combined, and accommodates a large number of terminals and requires a large number of wireless base station devices, such as personal mobile communication and wireless LAN. Optical links available for.

[0002]

2. Description of the Related Art In a conventional radio signal distribution system using an optical fiber, as shown in FIG. 7, a radio control station 5 and a radio base station 10 are connected to each other in a one-to-one manner, and further, for a downlink 8 and an uplink 9. As a result, one optical fiber was required each. The radio control station 5 includes a signal input port 1, a signal output port 2, a frequency multiplexer 3, a frequency demultiplexer 4, an electro-optical converter 6, and an optical detector 7. On the other hand, the wireless base station 10
Is a photodetector 11, an electro-optical converter 12, a high frequency amplifier 1
3, 14, a circulator 15, and an antenna 16, and transmits and receives a radio signal 17 to and from an information terminal (not shown).

A cascade configuration shown in FIG. 8 is known as another link configuration in which one radio control station accommodates a large number of radio base stations. In this figure, since a large number of radio base stations 101 to n are cascade-connected to the optical fiber link, the number of optical fibers directly connected to the radio control station 18 is small, and two transmission / reception pairs can be formed. In the link configuration of FIG. 8, a high frequency signal is transmitted from the wireless control station 18 to the wireless base station 1.
Each of the information terminals 01 to n accommodates a downlink 25, and a radio base station 101 to n multiplexes high frequency signals from the information terminals to transmit the radio signals to the radio control station 18.

FIG. 9 is a detailed diagram of the downlink in FIG. 8, in which the radio control station converts a large number of high frequency signals frequency-multiplexed in an electric stage into optical signals by an electro-optical converter 27 and cascades them. The data is transmitted to the connected radio base stations 101 to n. Further, in the radio base station 101, a part of the optical carriers is used by the photodetector 28 for high frequency signal detection, and the remaining optical carriers are transmitted to the next-stage radio base station 102. On the other hand, the high frequency signal detected by the photodetector 28 of the wireless base station 101 is amplified by the high frequency amplifier 29, then the desired high frequency signal f1 ′ is selected by the frequency selection circuit 30, and the high frequency signal f1 is selected by the radiator 31. 'Is transmitted to the information terminal. Thereafter, the high frequency signal is distributed to the wireless zones covered by each wireless base station by the same procedure.

FIG. 10 is a detailed diagram of the uplink in FIG. 8, in which optical carriers are fed from the light source 32 provided in the radio control station to the radio base stations 101 to n through the optical fiber. Further, the optical external modulators that modulate the intensity of the optical carrier included in each radio base station are connected in cascade, and the intensity of each optical carrier is sequentially modulated by the high frequency signal received by each radio base station. In FIG. 10, in the first radio base station 101, the high frequency signal f1 from the information terminal is received by the antenna 35, and the high frequency amplifier 34
After being amplified by, it is input to the optical external modulator 33 and converted into an optical signal. In the same procedure as below, the high frequency signal is frequency-multiplexed on the optical carrier in each radio base station and is supplied to the optical detector 36 of the radio control station. The optical detector 36 reproduces the supplied optical signal into a high frequency signal. To do.

[0006]

[Problems to be Solved by the Invention]
In the case of the link configuration according to (1), the radio control station 5 needs two optical fibers, an electro-optical converter and an optical detector, a frequency multiplexer, and a frequency demultiplexer between each radio base station. When the number of base stations becomes enormous, the configuration of the radio control station becomes complicated, and the cost increase is inevitable due to the increase in the number of parts. Further, in the link configuration according to FIG. 8, although the radio control station can be greatly simplified, it can be used for downlink and uplink.
Since there is a need for two optical fibers and a radio control station needs a light source for the downlink and a light source for the uplink, there is a limit to cost reduction.

The present invention has been made in view of the above circumstances, and it is possible to simplify the radio control station, to make it economical, and to reduce the size, and to simplify the radio base station.
An object of the present invention is to provide an optical link capable of constructing a highly flexible wireless signal distribution / multiplexing system.

[0008]

According to a first aspect of the present invention, in an optical link for converting a wirelessly transmitted high frequency signal into an optical signal and transmitting the optical signal, a plurality of first high frequency signals are received and the optical signal is transmitted. A first radio control station that converts the signal and transmits the signal, and the optical signal that the first radio control station transmits, and outputs a part of the plurality of first high frequency signals to the outside by a radio signal. Then, a second high frequency signal wirelessly transmitted from the outside and having a frequency different from any frequency of the plurality of first high frequency signals is received, and the second high frequency signal is added to the optical signal. A plurality of radio base stations to be superposed, and a second radio control station that detects a plurality of the second high frequency signals respectively superposed on the optical signal, the first radio control A plurality of wireless base stations are cascaded starting from a station. Continued, and an optical link characterized in that the end point of the second radio control station.

According to a second aspect of the present invention, the radio base station includes an optical detector for extracting the plurality of first high frequency signals from the optical signal, and a plurality of first high frequency signals extracted by the optical detector. A high-frequency filter for extracting only a first high-frequency signal of a predetermined frequency from the signal; a wireless signal transmitting means for transmitting the first high-frequency signal of the predetermined frequency extracted by the high-frequency filter to the outside as a wireless signal; Wireless signal receiving means for receiving the second high frequency signal wirelessly transmitted from the second wireless signal receiving means, and second wireless signal receiving means received by the wireless signal receiving means.
The optical link according to claim 1, further comprising: an optical external modulator that superimposes the high frequency signal of 1. on the optical signal.

According to a third aspect of the present invention, the radio signal transmitting means and the radio signal receiving means use the same antenna, and the first high frequency signal of the predetermined frequency extracted by the high frequency filter and the second high frequency signal. The optical link according to claim 2, wherein a high frequency signal is separated by a circulator. The invention according to claim 4 is the optical link according to claims 2 and 3, wherein in at least one of the radio base stations, the optical detector is a traveling wave type semiconductor optical amplifier.

According to a fifth aspect of the present invention, in at least one of the radio base stations, the optical external modulator is a traveling wave type semiconductor optical amplifier. is there. The invention according to claim 6 is characterized in that, in at least one of the radio base stations, the optical detector and the optical external modulator are one traveling-wave type semiconductor optical amplifier. It is an optical link. The invention according to claim 7 is the first radio control station and the second radio control station.
7. The optical link according to claim 1, wherein the optical link is a wireless control station including both of the wireless control stations.

[0012]

According to the present invention, since the radio control station and each radio base station are connected in cascade, it is not necessary to provide the radio control station with an electro-optical converter and an optical detector for each radio base station.
Therefore, it is possible to significantly reduce the parts and the like as compared with the conventional example. That is, the radio control station is characterized in that it can be configured only by opto-electric conversion or electro-optical conversion corresponding to one optical fiber. Further, since each wireless base station performs optical detection and optical modulation with the same optical fiber, the wireless control station has only one
Only one light source needs to be installed, and further cost reduction can be achieved.

Further, since one optical fiber is used for both transmission and reception, the radio base station can be simplified. That is, the radio base station is configured by using a cascade connection of an optical detector and an optical external modulator, and since it is an optical waveguide type device, it can be easily integrated. For example, in FIG. 7, since a light source is required for the electro-optical converter, each light source is installed in each radio base station. Therefore, there has been a limit to the cost reduction of the wireless base station. However, since the present invention does not require a light source for each wireless base station, it greatly simplifies the wireless base station,
Economicization can be achieved.

[0014]

An embodiment of the present invention will be described below with reference to the drawings. First, a first embodiment of the present invention will be described.
FIG. 1 is a diagram showing the configuration of an optical link in the first embodiment of the present invention. In this figure, an electro-optical converter 37 and an optical detector 45 are installed in the radio control station, and the electro-optical converter 37 sends a high frequency signal f to an information terminal (not shown).
1'-fn 'are frequency-multiplexed and converted into optical signals, and the photodetector 45 detects the high-frequency signals f1-fn transmitted from the information terminal in addition to the high-frequency signals f1'-fn'. An optical detector 38 having an optical input / output port and an optical external modulator 41 are cascade-connected in each radio base station to perform conversion between light and electricity. The high frequency signal detected by the optical detector 38 is converted by a high frequency amplifier 39. The amplified signal is amplified, and a desired frequency is selected by the frequency selection circuit 40, and is radiated into space through the circulator 43 and the antenna 44.

On the other hand, the high frequency signal transmitted from the information terminal is received by the antenna 44, input to the optical external modulator 41 via the circulator 43 and the high frequency amplifier 42. The optical external modulator 41 performs optical carrier output intensity modulation on the optical signal supplied from the optical detector 38 with the input high frequency signal, and transmits the optical carrier output intensity modulation to the next-stage radio base station 102. After the same operation is performed in other radio base stations, the output of the radio base station n at the final stage is the optical detector 45 of the radio control station.
Is input to each radio base station to reproduce the multiplexed high frequency signal.

As described above, the optical device of each radio base station is only the photodetector and the optical external modulator, and since the lightwave signal can be transmitted to the radio control station without the light source, the radio base station,
Furthermore, it plays a major role in simplifying the wireless signal distribution system and making it economical. Furthermore, if an ultra wide band optical detector and an optical external modulator are used, there is an advantage that a high frequency signal (microwave to millimeter wave) over a wide frequency band can be transmitted. Therefore, it is possible to configure a wireless signal distribution system capable of supplying a huge amount of information to information terminals in a wireless zone covered by each wireless base station. The first
Although the radio control station that transmits an optical signal and the radio control station that detects an optical signal are separately described in the embodiments, these functions may be provided in the same radio control station.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a diagram showing the configuration of an optical link in the second embodiment. As shown in FIG. 2, the second embodiment has an optical detector (for example, in FIG. 1) that each radio base station has in the first embodiment described above. The optical detector 38) of the wireless base station 101 in FIG. Since the optical devices in the above-described first embodiment are all passive devices, the level of the optical carrier decreases every time the optical carrier passes through the optical device. The traveling wave type semiconductor optical amplifier has an optical carrier amplifying function and an optical detecting function, and can be used also as an optical detector. The traveling-wave type semiconductor optical amplifier 47 in FIG. 2 also amplifies optical carriers, so that the optical loss due to the optical external modulator 53 can be compensated. Therefore, it is possible to greatly expand the area that can be covered as the number of wireless base stations increases.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 3 is a diagram showing the configuration of the optical link in the third embodiment. As shown in this figure, in the third embodiment, an external optical modulator (for example, the external optical modulator 41 of the wireless base station 101 in FIG. 1) included in each wireless base station in the above-described first embodiment is a traveling wave semiconductor. It is replaced with the optical amplifier 62. Thereby, when a high frequency signal is applied to the traveling wave type semiconductor optical amplifier, the intensity modulation of the optical carrier can be performed. Further, the gain of the traveling wave type semiconductor optical amplifier can compensate the optical loss due to the photodetector. This effect is similar to that of FIG. 2 in the second embodiment described above.

Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 4 is a diagram showing the configuration of the optical link in the fourth embodiment. As shown in this figure, the optical device in the fourth embodiment is only the traveling wave semiconductor optical amplifier 65. The traveling wave type semiconductor optical amplifier has the light detecting function and the light modulating function as already described in the second and third embodiments. In the fourth embodiment, the traveling wave type semiconductor optical amplifier is The link configuration uses these functions at the same time.

In this figure, the radio control station has a frequency f
1'-fn 'are converted into an optical signal and transmitted to the wireless base station 101 via an optical fiber. The radio base station 101 amplifies the optical carrier by the traveling wave type semiconductor optical amplifier 65 and, at the same time, detects a high frequency signal from the optical carrier signal. The detected high frequency signal is circulator 66, high frequency amplifier 6
The frequency f1 ′ is transmitted to an information terminal (not shown) via the frequency selection circuit 68, the circulator 69, and the antenna 70.

The radio base station 101 receives the frequency f1 transmitted from the information terminal by the antenna 70, and the received frequency f1 is circulator 69 and high frequency amplifier 7.
1. It is input to the traveling wave type semiconductor optical amplifier 65 via the circulator 66. In the traveling wave type semiconductor optical amplifier 65,
The optical carrier is emphasized and modulated by the input frequency f1 and transmitted to the next-stage radio base station. Hereinafter, the same operation is performed in each radio base station, and finally the radio base station n
Is transmitted to the photodetector 72 of the radio control station via the optical fiber, and the photodetector 72 reproduces the high frequency signal multiplexed in each radio base station. As described above, since the optical function is realized only by the traveling wave type semiconductor optical amplifier, it is possible to simplify the optical circuit section and to make the radio base station economical.

Since the traveling wave type semiconductor optical amplifiers described in the second to fourth embodiments have the optical output-bias current characteristic shown in FIG. 5, by superposing the high frequency signal on the bias current. Intensity modulation of light can be performed. Further, FIG. 6 shows the optical input vs. detection current output characteristics of the traveling wave type semiconductor optical amplifier. As shown in this figure, since the detection current value changes depending on the optical input level, the intensity-modulated optical input signal changes to the high frequency signal. Can be detected. It goes without saying that a radio base station dedicated to reception and a radio base station dedicated to transmission can be added to the configurations of the optical links of the first to fourth embodiments described above.

[0023]

As described above, according to the present invention,
Since the wireless signals are distributed to many wireless base stations connected in cascade, and the wireless signals are multiplexed in each wireless base station, the wireless control station has only one optical detector and one electro-optical converter. Therefore, even when a large number of wireless base stations are accommodated, it is possible to greatly simplify the wireless control station and make it economical. Further, it is not necessary to provide each wireless base station with a light source for electro-optical conversion, so that the configuration of the wireless base station can be greatly simplified, and as a result, the economy of the entire system can be achieved. Further, the application of the traveling wave type semiconductor optical amplifier has an effect of improving the optical loss, thereby increasing the number of radio base stations and expanding the area which can be covered by one radio control station.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an optical link according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an optical link in the second embodiment.

FIG. 3 is a block diagram showing a configuration of an optical link according to the third embodiment.

FIG. 4 is a block diagram showing a configuration of an optical link according to the fourth embodiment.

FIG. 5 is a diagram showing optical output vs. bias current characteristics of a traveling wave semiconductor optical amplifier.

FIG. 6 is a diagram showing optical input vs. detection current output characteristics.

FIG. 7 is a block diagram showing a configuration of a conventional optical link.

FIG. 8 is a block diagram showing another configuration of a conventional optical link.

FIG. 9 is a block diagram showing in detail the configuration of the downlink in FIG.

FIG. 10 is a block diagram showing in detail the configuration of the uplink in FIG.

[Explanation of symbols]

37, 46, 55, 64 ... Electro-optical converter, 38, 4
5,54,56,63,72 ... Photodetector, 39,4
2, 48, 52, 57, 61, 67, 71 ... High-frequency amplifier, 43, 50, 59, 66, 69 ... Circulator, 44, 51, 60, 70 ... Antenna, 41, 53
... Optical external modulator, 40, 49, 58, 68 ... Frequency selection circuit, 47, 62, 65 ... Semiconductor optical amplifier

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H04B 10/20 H04B 9/00 N

Claims (7)

[Claims] 1. An optical link for converting a wirelessly transmitted high frequency signal into an optical signal for transmission, and a first wireless control station for receiving a plurality of first high frequency signals, converting the optical signals into the optical signals, and transmitting the optical signals. And receiving the optical signal transmitted by the first radio control station,
A second radio signal that outputs a part of the plurality of first high frequency signals to the outside, is wirelessly transmitted from the outside, and has a frequency different from any frequency of the plurality of first high frequency signals. A plurality of radio base stations that receive a high frequency signal and superimpose the second high frequency signal on the optical signal; and a plurality of second high frequency signals that the plurality of radio base stations superimpose on the optical signal. A second radio control station for detecting, wherein the plurality of radio base stations are cascade-connected from the first radio control station as a starting point, and the second radio control station is an end point. Link. 2. The radio base station comprises: a photodetector for extracting the plurality of first high frequency signals from the optical signal; and a predetermined one of the plurality of first high frequency signals extracted by the photodetector. A high-frequency filter for extracting only a first high-frequency signal of a frequency, a wireless signal transmitting means for transmitting the first high-frequency signal of a predetermined frequency extracted by the high-frequency filter to the outside as a wireless signal, and wirelessly transmitted from the outside. A radio signal receiving means for receiving the second high frequency signal, and a second high frequency signal received by the radio signal receiving means,
The optical link according to claim 1, further comprising an optical external modulator that is superimposed on the optical signal. 3. The radio signal transmitting means and the radio signal receiving means use the same antenna, and use a circulator for the first high frequency signal and the second high frequency signal of a predetermined frequency extracted by the high frequency filter. The optical link according to claim 2, wherein the optical link is separated. 4. The optical link according to claim 2, wherein in at least one of the radio base stations, the optical detector is a traveling wave type semiconductor optical amplifier. 5. The optical link according to claim 2, wherein in the at least one radio base station, the optical external modulator is a traveling wave type semiconductor optical amplifier. 6. The optical link according to claim 2, wherein in at least one of the radio base stations, the optical detector and the optical external modulator are one traveling wave type semiconductor optical amplifier. 7. The optical link according to claim 1, which is a radio control station including both the first radio control station and the second radio control station.